Fuel control



March 7, 1961 C. F. STEARNS ETAL 3,307,352

v l FUEL CONTROL Filed Jani 15, 1964 4 sheets-Sheet 1 March 7, 1967 c. F. sTEARNs ETAL 3,397,352

FUEL CONTROL 4 Sheets-Sheet 2 Filed Jan. 15, 1964 y q y un. mw

4 Sheets-Sheet 5 FUEL CONTROL C. F` STEARNS ETAL.

March 7, 1967 Filed Jan. l5, 1964 l United States Patent Office 3,?@73552 Patented Mar. 7, 1967 3,307,352 FUEL CONTROL Charles F. Stearns, East Longmeadow, Mass., Louis A. Urban, Granby, Conn., and Robert C. Baker, Bedford, Mass., assignors to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Filed Jan. 15, 1964, Ser. No. 337,837

13 Claims. (Cl. l60-39.28)

This invention relates to fuel controls and more particularly t-o fuel controls for controlling turbine types of power plants.

As is generally well known in the art, the fuel control is a combination of metering devices and computing mechanism serving to control the flow of fuel to the engine in an amount commensurate with efficient and optimum engine operation, yet lassuring that a'malfunction due to surge, rich or lean flame out and overtemperature does not ensue. Overtemperature in this instance means that temperature which will adversely affect the components of the engine.

Basically, the metering system of the fuel control selects the rate of fuel flow to be supplied to the engine burners in accordance with the amount of thrust (for pure jet) or horsepower (for tu'rboprops and jets driving va variable load such as the rotor blades of a helicopter) demanded by the pilot, but subject to engine operating limitations as scheduled by the computing system as a result of its monitoring various engine operational parameters. As is realized, the computing system of the fuel control senses and combines the various parameter to control the output of the metering section during all regimes of engine operation.

In the heretofore known fuel controls for turbine power plants, such as the type described and claimed in Patent No. 2,822,666 granted to S. G. Best, engine scheduling is accomplished by relating all the operational parameters being monitored by the fuel control in terms of scheduled ratio of Wf/Pa, where W1 is fuel iiow in pounds per hour, P3 is absolute compressor discharge pressure. It is important to understand here that this ratio of Wf/Pa is a value built into the fuel control by virtue of cams, linkages, levers and the like which value represents the desired engine operation. Hence, the ratio Wf/PS may be considered to be a scheduled value, which for any given speed (rpm.) of the engines rotor (compressor and/or turbine) defines all the operations of the engine.

In these heretofore fuel controls utilizing the Wf/P3 control parameter, the computing mechanism computes the various monitored engine operation parameters and converts these parameters in terms of this Wf/Pg ratio. The fuel control also senses the actual compressor discharge pressure and feeds this signal to the multiplying mechanism of the computing system which also receives the Wil/P3 ratio signal. Here these two signals are multiplied for obtaining the product Wr of the two. This Wt signal is then transmitted to the fuel metering devices for metering sufficient amount of fuel to produce the desired thrust or horsepower. Basically, such a system describes the control philosophy for both acceleration and steady state engine operation.

As is known in this art, the highest obtainable rate of acceleration is always desirable in turbine types of power plants, and obviously, this is accomplished by placing the metering devices in their full flow position. Owing to the fact that the component parts of the engine can only tolerate a certain maximum temperature and that the compressor is subject to surge (a pressure pulsating condition that occurs at any particular given speed, at a given pressure ratio or given weight flow of the compressor) the computing system must assure that these conditions as well as rich and lean flame out do not ensue. These regimes of operation are computed by the fuel control computing system which senses and combines various engine operating parameters.

The heretofore system such as the one noted in the Best patent, supra, utilizes a three-dimensional cam for computing the fuel rate necessary to avoid the maximum temperature and surge. The three-dimensional cam is best described as a cam having movement in an axial and rotational direction in response to selected engine operating conditions and operates to give the temperature and surge limits. As mentioned above, the fuel control' com puting system must compute the value of the preselected engine operatic-nal parameters in terms of Wf/P ratio so that it will be compatible with the multiplication system. The three-dimensional cam serves this purpose for acceleration scheduling. This is accomplished by having the cam move in one direction in response to compressor speed and having it move in another direction in response to compressor inlet temperature. The cam follower resp-onding to the radius of the cam develops a signal whose value corresponds to the desired Wf/Pg value.

The cams prole comprises a plurality of curves superimposed thereon defning the engines operational characteristics in terms of Wf/P3 as a function of inlet temperature of the compressor and compressor speed. To more fully appreciate the present invention, it is worthy to note that the engines surge and temperature characteristics can be defined for all engine operations in terms of Wf/Pg vs. engine speed. In such a plot it will be appreciated that both surge and tem-perature form a family of curves where each curve of the family depends on the value of the compressor inlet temperature. As is obvious to one skilled in this art the turbine inlet temperature for any given speed of the compressor and value of Wf/Pa varies as -a function of compressor inlet temperature.

As is well known by those familiar with the heretofore known fuel control, surge and temperature limits are each represented by a family of curves for the overall engine operation. It is also well known that the conventional three-dimensional cam was the only known practical device capable of defining a schedule representing two separate families of curves varying as a function of two independent input signals. Owing to this fact, it has been the heretofore practice to utilize a three-dimensional cam in this heretofore known fuel control.

It is a purpose of this invention to completely eliminate the three-dimensional cam yet obtain accurate acceleration limit scheduling mechanism. We have found that this is made possible by utilizing Wf02X/P3 versus N2/02 or N /Vbg as the control parameters instead of the heretofore known Wf/Pg versus N control parameters; where :the r.p.m. of engine rotating mechanism; 92=temperperature of the air upstream of the compressor and x=an exponential value.

By utilizing the WfZX/Ps vs. N2/02 as the control parameters, the maximum temperature limit schedule and surge limit schedule can each be represented by a single function of the parameters. This is a complete departure from the heretofore known fuel control philosophy since as was described above, the family of curves representing surge and temperature become nonexisting. Owing to this fact the need of a three-dimensional cam is completely eliminated.

It will be appreciated that the elimination of the threedimensional ca-m is a major break-through in this art [derivation of the control parameter.

l FIG. 2 is a schematic illustration showing a fuel control connected to a free-turbine type of gas turbine engine. `v FIG. 3 is a schematic illustration of a fuel control mechanism utilizing this invention.

FIG. 4 is a graphical illustration representing the operational characteristics of a fuel control made in ac-l cordance with this invention. p FIG, 5 is a schematic of a hydraulic circuit illustrating a hydraulic multiplication system. l

FIG. 6 is a schematic of a hydraulic circuit illustrating an addition-al multiplication function of a hydraulic multiplication system.

FIG. 7 is a partial schematic showing a modification of FIG. 3, and

FIG. 8 is -a block diagram illustrating the invention.

In order `to a-ppreciate this invention it is necessary to understand that the maximum temperature limit schedule of a gas turbine engine can be represented by a single function of the parameters WfgX/P?J and N/ V672 and that the surge -limit schedule can be represented by a single function of the parameters Wf/Pav' and N/V.

Thus, the problem solved by this invention is to modify the Wf/Pa lparameter which changes with varying compressor inlet temperature to obtain constant turbine inlet temperature at any given corrected speed, i.e., N/VE.. It is within the scope of this invention if the terms (parlameters) are computed in sta-tic or total values.

The following mathematical derivation shows how the engine characteristics have been computed to show that a single line function of Wf02X/P3 versus corrected engine speed will h old actual turbine inlet temperature at a constant value for any value, of engine inlet temperature. .Small second order effects have been ignored in the deriva. tion. fr. The Ifollowing notations will be used for deriving the parameter WHZX/Pa-z rise in deg-ree Units/ pound Rankine,

Constant, =Sign for derivative.

The subscripts listed below indicate the location within the engin-e unless indicated otherwise where:

2 is at the inlet of the compressor, 3 is at the outlet of the compressor, 4 is at the inlet of the turbine, 5 is at the discharge of the turbine, 6 is at the tailpipe, b is at the burner. Y

To satisfy the requirement stated immediately above, first it is necessary to find the interrel-ationship that exists between the corrected ratio unit Wf/PgV'HZ and corrected turbine inlet temperature T 4/ 02 at any particular corrected engine speed N 02.

Turbine inlet -air flow is commonly expressed as a ow number F4, where 1) r :Wa/

t A412., j Using the calculus this may be differentiated to the form 2 gauw@ twang@ r4 Wg 2 T.4 P., A.

Recognizing that the turbine inlet area is of fixed geometry, and ignoring minor second order effects, this may be reexpressed as P3 W, T4 r4 The general expression for ratio units in terms of other parameters within the engine is (the calculus. used is taken from the standard form for differentiating where dwlog u=du/u. If u=x.y.z, then log u :log x-l-log y-i-log z and du dm d n +3?! The burner temperature rise is simply (6) MFL-T3 The rate of change of rburner temperature rise is then '(7) angl. T3 L.

AT1, ATb T4 AT1, T3

For an `adiabatic compression as occurs in a gas turbine engine compressor, the compressor temperature ratio is approximately (8) I@ n e) Km This may be differentiated to the form 9 an: K-1 m T3 K'lo P3 (This form was `obtained lby differentiating using the forni log lu=a= u: tzr-Xgl h nced-u-a@) P2-K17.e u :v

Equations 7 and 9 may be combined to the form (10) ATb: T4 4 l3 Kll3 AT1, ATb T4 AT1, K11., P3 Equations 10 and 5 may be combined to the form Combining Equations 11 and 3 and collecting similar terms Equation 12 then is a 4general expression for the rate of change of ratio units in terms of the rates of change of the turbine inlet flow number, turbine inlet temperature and engine inlet air flo-w. At any constant corrected e11- gine speed (which is a condition of the original problem statement) there is very little, if any, variation of turbine inlet ow number due to changes in any other thermodynamic parameter, especially when the turbine nozzles are choked, as they are in most engines over the greatest part of their useful operating spectrum. Equation 12 may therefore be simplied to To get the desired expression for the rate of change of ratio units in terms of the rate of change of turbiner inlet temperature, lit is necessary to establish the relationship between the rat-es of change of air How and turbine inlet temperature at constant corrected speed. In the art, compresor performance is commonly depicted in a graphical chart form called a compressor map or compnessor characteristic. FIG. l will be recognized as a portion of such a compressor map, showing a portion of a single corrected speed line and two turbine inlet temperature lines A and B. Value C is the change in engine air flow which will occur when going from turbine inlet temperature value A to value B at constant engine speed. Value D is lthe change which `would occur in compressor pressure ratio going from turbine inlet temperature value A to value B at constant engine air flow. Obviously then 6 From Equation 3 and the problem statement it is obvious that is the reciprocal of the absolute value of the slope of the compressor map speed line.

Using Equations 17, 18 and 19, Equation 16 may then be expressed as Using the corrected quantity equivalents of the parameters, Equation 21 may be expressed as Equation 22 then expresses the interrelationship that exists between the corrected ratio unit Wf/P3\/02 and corrected turbine inlet temperature T4/02 at any particular corrected engine speed N/\/02, with minor second order terms being ignored.

The differentialform, Equation 22 may now be expanded to Since the desire is to -nd a single value function of Wf/Pa and 02 which will hold actual T4 constant regard- Letting the coefficient between the brackets he represented `by the arbitrary symbol x and using the calculus to integrate Equation 24 WIHZX costant That is to say, if at any particular value of corrected engine speed a constant value of Wfzx/PB is scheduled to the engine, then actual turbine inlet temperature will not vary regardless of the value of engine inlet temperature ratio 02. The actual value of ratio units scheduled to the engine will be l/Vfxgll Ps- P3 02x As can be seen from Equation 24 the x exponent contains terms related to -burner temperature rise, compressor discharge temperature, compressor efficiency, and the slope of the compressor characteristic curves, all of which vary with corrected engine speed for any particular turbine inlet temperature. IFor many engines it would be sufficiently precise to let x be a constant irrespective of corrected engine speed; for others it would not, and x itself must also be varied withcorrected engine speed, as is Wf62x/ P 3.

Referring now to FIG. 2 showing a gas turbine engine generally illustrated by numeral ly having a first section 12, wherein the compressor is driven by turbine section 16. Since the turbine 16 is connected to compressor 12 l for driving the same, it is generally referred to as the gas generator turbine and the rotational speed thereof is `hereinafter referred to as Ng. Turbine 18 illustrates a free turbine which may be adapted to drive a variable load such asa helicopter rotor', propeller and the like. Since turbine 18is mechanically disconnected from turbine 16 suitably situated in the cabin of the aircraft and are available to the pilot for setting the speed of the gas generator and the speed of the free turbine in a manner to -be described hereinbelow. These control levers also serve to operate various other mechanically movable parts in the fuel control, also to be described hereinbelow. Thus, lever 42 rotates gear 46 which rotates the connecting shaft and lever 44 rotates gear 43 which rotates its connecting rotary shaft.

While the fuel control showing the preferred embodiment is illustrated in connection with a free turbine type of gas turbine engine, it is to be understood that this invention has applications as will become obvious to one skilled in the art in connection with all types of gas turbine engines. As is known in this art, the free turbine can operate at a different speed than the gas generator. By virtue of this fact, it is often desirable to measure Nf as well as Ng. If, however, it is desirable to utilize this invention in connection with a solid shaft or a coupled type of gas turbine engine, it would only lbe necessary to sense the speed of one of the rotating mechanisms within the engine. In this event, the free turbine speed sensor which |but is driven by the discharging gases thereof and because v it is free or hasionly an aerodynamic connection with the turbines in the rst turbine section, it is generally referred to as the free turbine and the speed thereof is hereinafter referred to as Nf. Interposed between the compressor section and the turbine section is the burner section generally indicated by numeral 20. Fuel is injected into the burner section through the fuel manifold 22 `which is regulated by the fuel metering section generally indicated by numeral 24 to be described hereinbelow.

Basically, the fuel metering system of the fuel control serves to meter fuel to the engine in an amount commensuratewith optimum engine operations whilefassuring that malfunctions due to surge, overtemperature or rich or lean blow out do not ensue. Fuel is fed to fuel control 24 from reservoir 26 and the pressure thereof is increased 'by virtue of pump 28 through line 30. The fuel control also contains a drain manifold which discharges excessive fuel or ported fuel to drain via line 32.

The fuel control also contains a computing system which measures certain parameters, computes them in accordance with the controlvparameters indicated in the above for controlling the fuel metering system. For this purpose, compressor inlet temperature is sensed via line 34, compressor speed (Nglis sensedvia line 36, compressor discharge pressure is sensed via line 38 and free turbine speed (Nf) is sensed via line 40. It is to be understood that any suitable mechanism for sensing these various operating conditions of the engine is contemplated within the scope of this invention. Power levers 42 and 44 are will be described hereinbelow would not be utilized.

It is also to be understood and will be obvious to one skilled in the art that the terminology of power lever is not particularly limited to the particular lever in the cockpit of the aircraft. Rather, it is intended to cover any linkage connecting the cockpit to the fuel control whether it be referred to as a go handle, power lever or throttle lever or the like.

Now referring to FIG. 3 which is a schematic illustration of a fuel control designated .by numeral 24 as having both a fuel metering system and a computing system. Fuel is admitted to the throttle valve `generally indicated by numeral 50 via inlet or supply line 30. Throttle valve 50 comprises spool 54 having a fluid reaction end S6 and a combined pressure and a spring reaction end 58. Adjustable spring 60 acts against end 5S while fluid admitted into chamber 62 acts against end 56 and obviously the force generated by the pressure in chamber 62 and the force Vgenerated by spring 6i) and the pressure acting on end 58 will determine the position of spool 54, Fuel admitted to valve Si) from line 30 is metered Iby the metering edge 64 on spool 54 into line 22 by way of passage 66 and minimum pressure and shutoff valve generally indicated by numeral 68.

Minimum pressure and shutoff valve 68 comprises valve member 70 urged in one direction by the spring 72. When the value of the pressure acting on the underside or the left-hand end of valve member 70 is sucient to overcome the force exerted by spring 72 as well as the pressure in chamber 74, the valve mem-ber is unseated allowing communication Ibetween line 66 and line 22.

As noted from FIG. 3, solenoid 76 normally urges ball valve 78 so that line 86 interconnects chamber 74 with drain p-ressure P0 via clearance around valve stem 82 so that drain pressure and theforce of spring 72 act on one end of valve member 70 opposing the force of the metered fuel discharging from line 66. Solenoid 76 may be actuated by the pilot by depressing button 81 which conducts electrical current to actuate the plungers 82 and 84. Plunger 82 in this instance would move to the right seating ball 78 against the drain line, interconnecting line and line 86. This serves to direct pressure upstream of throttle valve SG lbehind valve element 70 for urging this valve in the closed position for changing to the emergency engine fuel flow.

So that the displacement of valve 50 and metering edge 64- is directly proportional to the fuel passing therethrough, pressure regulator valve generally indicated by numeral 88 is employed. Valve 88 comprises a spool 90 mounted in cylinder 92 defining a pair of opposing charnbers 94 and 96. Disposed in chamber 94 is adjustable spring 99. Fluid upstream and downstream of throttle valve 50 is admitted to chambers 94 and 96 through line 98, valve 100 and line 102 in one instance and line 104, ball valve 106 and lines 86 and 89 in the other instance. It will be noted from the drawing that valve 106 is seated on the left end blocking flow between drain and line 104 while admitting pressure upstream of 50 into chamber 96.

From the foregoing, it is apparent that valve member 90 is subjected to upstream and downstream pressure together with the force exerted by spring 99. This serves to position the metering portion 108 relative to orice 110. This orifice and metering element 108 serve to bleed pressure fluid upstream of valve 50 through line 112 into line 114 and eventually 'back to the reservoir through line 32, bypassing the throttle valve. Thus, it is apparent that the pressure drop across throttle valve 50 is maintained at a constant value, which value is determined by the force or the strength of spring 99. In the event a deviation of the desired pressure drop is evidenced, valve element 90 will move relative to the metering edge 110 for opening or closing said valve and hence increasing or decreasing the rate of flow therethrough for regulating the pressure drop across valve 50 to hold it constant.

It will be noted that valve 100 which is connected to lever 42 and rotated thereby is normally in the open position. By rotating valve 100, fluid in line 102 is ported to drain via line 118. This decreases the pressure in chamber 94 and since the pressure acting on the other end is at a greater value, it permits the valve to move toward the right in the full open position. This bypasses the fuel around the throttle valve and directs the entire fuel back to drain. This completely starves the engine and prevents the fuel from increasing to a pressure whose valve would be above the structural integrity of the components of the fuel control. Overpressurization is occasioned by virtue of the fact that if the engine windmills by virtue of the air passing over the compressor, the fuel pump driven thereby would begin to overspeed and build up the pressure in line 30. What has just been described is the normal or main fuel regulating means of the fuel control. This fuel control may also include an emergency system comprising shutoff valve 120, emergency throttle valve 133, emergency pressure regulating valve 134 and valves 106, 78 and 137 (note however, that valve 137 is only to shutoff the emergency system).

Of course, the emergency fuel control portion is only actuated in the event that the normal fuel control becomes inoperative for one reason or another. In that event, switch 81 is actuated for energizing solenoid 76 for shifting the position of ball valves 78 and 106. This leads fluid from chamber 96 to drain via lines 104 and 83, leads fluid from chamber 140 to drain via lines 143, 104 and 83 While chamber 74 is connected with high pressure via lines 86 and 80 for directing valve member 72 to the closed position. Valve 133 is opened and is directly coupled to lever 42 for metering fluid to the engine through'valve 120 and line 22. By virtue of the fact that the pressure underneath the valve element 146 is greater than both the spring force and the pressure in chamber 140, it shifts to the open position allowing the communication between valve 133 and line 22. Further, it will be appreciated that at this time valve 137 is directed to communicate line 148 to line 147 and allowing normally closed emergency pressure regulating valve 134 to open. This Valve then serves to control the pressure drop across valve 133. Now that the fuel regulating system has been described, the next portion of the description will -be directed to describing the computing mechanism of the fuel control.

As was mentioned above, the position of spool 54 of throttle valve 50 is lpositioned by the pressure of the fluid in chamber 62. This pressure is made proportional to the desired amount of fuel which will operate the engine at a scheduled value determined by the fuel computing systern. The fuel computing system computes steady state and acceleration schedules as Will be described hereinbelow. In accomplishing this, levers 42 and 44 are positioned in the desired position to develop the desired amount of thrust or horsepower necessary to propel the aircraft for its desired operation. Referring now to lever 42 which serves to select the predetermined speed setting of the gas generator by virtue of setting the metering area dened by orifices and 132 of valve 134. This serves to set a desired area which will control the pressure in lines 136 and 138 by bleeding iluid to drain. Ignoring for the moment the valve generally indicated by numeral 140, this pressure, in turn, establishes the pressure in line 142. A pair of adjustable orifices 144 and 146 disposed in lines 136 and 138 respectively, serve to provide the idle and topping Ng limits by virtue of the fact that orice 130 is closed when lever 42 is set for topping and orifice 132 is closed when lever 42 is set for idle.

From the foregoing it is apparent that valve 134 determines a porting area for establishing a pressure in line 142 which is proportional to the speed error of the gas generator compressor 12. In order to establish a signal to compare the desired speed with actual speed, speed sensor generally indicated Iby numeral 150 is employed and suitably connected to and driven by compressor 12 for rotating platform 152. The platform contains ilyweights 154 and 156 which are pivotally co-nnected to the upstanding members 158 and 160. The arms of the flyweights bear against an end of pilot valve 160. When the ilyweights are disturbed from their vertical position resulting from the rotational movement of platform 152, they will either move inwardly or outwardly relative to the rotational axis for positioning valve 160. This, in turn, meters fluid from line 162 to line 142 upstream of fixed restriction 166 proportional to the square of the speed. It will be noted that the pressure in line 142 goes to chamber 163 via annular space 165 made at the lap fit Ibetween spool 161 and its cylinder and balances the flyweight force which nulls the valve 161 at the right pressure.

It is apparent from the foregoing that the pressure in line 142 downsrteam of orifice 166 is a function of the actual speed of the compressor and the desired speed generated by the position of lever 42. This value which is a speed error signal acts on the underside of valve 168 for positioning the metering edge 170.

From the drawing it will be apparent that compressor discharge pressure from line 38 is admitted internally of bellows 172. The free end of bellows 172 acts against pilot valve 174 which serves to regulate pressure in line 176 as a function of compressor discharge pressure. This is accomplished -by metering fluid issuing from pressure supply line 173 through passages in spool 174 and into chamber 175 via lines 178. Spool 174 is counterbalanced by the pressure in chamber 175 acting on its underside. Spool 174 translates with respect to the opening 180' until the pressure in chamber 175 acting externally of bellows 172 balances the pressure and the spring acting internally thereof. At the point of equilibrium, the pressure in line 176 is established at the point where it is proportional to compressor discharge pressure plus a constant.

This pressure line 176 is then fed into pilot valve 168 which serves to -rneter it to line 180. By properly contouring metering edge 170, this pressure is Ithen made a function of the desired fuel flow or Wf for steady state operation. The fluid metered by metering edge is then fed into selector valve 182 via branch line 184 where it is admitted to chamber 62 through line 186 when spool 1'88 is in the righthand position.

The position of lever 44 serves to generate a signal which will produce a value for establishing the speed at which the free turbine is desired to operate. This is accomplished by the rotation of valve 201 which establishes an area across orifices 202 and 204 venting fluid out of chamber 206 formed in valve 140. This serves to control the pressure drop across restrictor 208 for establishing the desired Nf. Adjustable restrictions 210 and 212 downstream of orifices 202 and 204 respectively establish the lminimum and maximum speed of the free turbine. The pressure upstream of restrictor 208 is proportional to the square of the speed of the free turbine which is estab lished by pilot valve 210. This valve operates substantially the same as valve 150 by coupling platform 213 to the free turbine shown by line 40 in FG. 1 so that ilyweights 214 responding to this speed position pilot valve 211. This meters fluid issuing from servo supply line 216 into line 218 in such a manner as to make this pressure proportional tothe free turbine speed square. Hence, the pressure in chamber 206 is established as being the difference between the actual speed generated by pilot valve 211 and the desired speed established by the position of lever 44.

From the foregoing it is apparent that spool 220 is positioned as a function of speed error for modifying the pressure in line 142. This has the effect of resettin-g the position of spool 168 and hence establishing a. new value for the setting of the gas `generator or Ng. What has just been described is the steady state operation as established by the computin-g mechanism of the fuel control. The next portion of the description will describe the established acceleration surge and overtemperature schedule of the computing mechanism.

As noted from FIG. 3, pressure proportional to compressor discharge pressure is admitted to temperature responsive valve generally indicated by numeral 200 through line 222. The metering edge 224 formed on spool 226 is made to vary as a function of the square root of 02. Compressor inlet temperature admitted to act externally of bellows 228 through line 34 causes it to expand or contract for positioning spool 226 as a function of compressor inlet temperature. By virtue of positioning meterin-g edge 224, the pressure drop across restrictor 230 which bleeds fluid from line 232 to drain is controlled and a multiplication is elfectuated so that the pressure in line 232 is made proportional to compressor discharge pressure and a function of the square root of 02. This pressure is then admitted to valve 234 which is positioned as a function of the speed Ng2/62 in the manner to be described hereinbelow, Metering edge 238 of spool 240 is made to define an area which is a function of The combination of this area and the area established by fixed restrictor 242 serves to effect another multiplication so that the pressure in line 244 is made proportional to the desired fuel flow Wp The pressure in line 244 is then admitted into selector valve 246 to act on the left end of spool 248 which in this instance is the desired Wf for establishin-g the surge limit of the schedule. The pressure acting on the right end of spool 248 is the limit in terms of W1 for the temperature limiting portion of the acceleration schedule. This is established by metering lands 250 of spool 226 and 252 of spool 240 in the manner described immediately below.

Fluid pressure proportional to compressor discharge pressure evidenced in line 176 is admitted to the metering land 250 through line 256. This metering land is made a reciprocal function of 02 raised to the "x power which x power is established according to the mathematical computations noted above. Hence, the pressure established in line 258 is a multiplication by virtue of metering edge 250 and fixed restriction 260. The area defined by metering edge 250 varies as a function of compressor discharge pressure times a function of l/02X. This fluid is then admitted to valve 234 where metering edge 252 in conjunction with fixed restriction 262 serves to effect another multiplication. Since the area defined by metering edge 252 is a function of Wf/Pa times 02X, the pressure in line 264 is proportional to the desired fuel flow (Wf) for limiting temperature.

This fluid in line 264 is then admitted to selector valve 246 to act on the right-hand end of spool 248. The difference between the two values of the pressures acting on either end of spool 248 determines the position of spool 248 to either the left or right for admitting fiuid into line 266. Hence, the pressure in line 266 is either the desired Wi surge or the desired Wf temperature depending on the position of selector spool 248 of selector valve 246. This pressure is then admitted to act on the left end of spool 188. As mentioned above, steady state pressure proportional to the desired fuel flow (Wf) acts on the right-hand end. The difference between the two values will position spool 188 to either the left or right. The pressure proportional to lthe desired steady state Wi or the desired surge Wi or the desired overtemperature Wf is then admitted to chamber 62 for controlling the position of spool 54 of throttle valve 50. v

Since it is desirable to compute the terms of the parameters in absolute values rather than gauge pressure values, absolute pressure control 280 is employed. Fluid from the various computating valves and restrictions which is eventually ported to drain is first admitted into chamber 282 via line 284 -where it acts externally of bellows 286. Bellows 286 is evacuated and has its free end operatively connected to one end of spool 288. Since the -other end of spool 288 is counterbalanced by the pressure admitted thereto through line 290 metering edge 292 thereof will assume a position to establish the drain pressure for establishing an absolute value datum line. Note that the pressure level is set equal to the spring constant established in valve 171. Therefore, it will be appreciated that the datum line is equivalent t-o an absolute value so that the pressure control valves use a zero pressure datum rather than a gauge pressure datum.

As was pointed out in the above, the exponential x for certain engines must be varied with the corrected engine speed. Mechanism for accomplishing this is shown in FIG. 7. Basically the acceleration computing mechanism shown in FIG. 3 may be slightly modified to perform this function. This may be accomplished by adding a single land to spool 226 of valve 200 and two lands to spool 240 and slightly rearranging the fluid connecting lines. Like numeral references correspond to like parts in the various drawings. Spool 240 like spool 240 of FIG. 3 is positioned as a function of N2/02. This is achieved by developing pressure acting on the underside of spool 240 to a value proportional to this term by directing fiuid from lline 142 into line 255 by passing it through orifice 251 which modifies the pressure from line 142. Since the pressure upstream of restriction 166 is a function of the speed of the governor (see FIG. 3) and since the area defined by metering edge 251 is 'a function of temperature, the computing system serves to develop pressure in line 255 and charnber 302 to be equivalent to a function of N2/02.

In order to obtain the surge limit, pressure proportional to P3 is bled from line 176 through line 256 and restriction 306. The pressure downstream of fixed restriction 306 is controlled by the metering edge 308 formed on spool 240 which communicates line 256 to drain via lines 310 and 312. Metering edge 30S is designed to cooperate witlh its metering port so that it defines 4a metering area which is a function of Wf/PBV'H; The cooperation between metering edge 308 and fixed restriction 306 effectuates a multiplication for establishing thi pressure intermediate thereof to be a function of Wf/x/z. The pressure across fixed restriction 314 disposed in line 310 is controlled by metering edge 316 formed on spool 226 which serves to port fluid to drain via line 318 for establishing the proper pressure level in the line intermediate thereof. The metering edge 316 i3 cooperates with its registering port to establish an area which is a function of the V02. This variable restriction together with the fixed restriction 314 cooperate in such a manner as to effectuate a still further multiplication of the'Wf/Vz pressure to obtain a pressure which is proportional to the desired fuel flow Wt which value is the surge limit established by the computating system.

This pressure is then bled H through branch line 320 and directed to valve 246.

The next portion of the description will be concerned with the mechanism for generating the temperature limit signal to valve 246. Fluid Whose pressure is equivalent to compressor discharge pressure is bled from line 176 through line 222 and restriction 322 and directed through line 326 to metering edge 324 formed on spool 240. The area defined by metering edge 324 cooperating with its registering port is made a function of WfzX/Pg. This metering edge position serves to communicate line 326 wit'hJdrain line 328 for controlling the pressure drop across restrictor 322 for developing a pressure intermediate thereof at a value proportional to Wf02x. A pair of parallel disposed lbranch lines 330 and 332 bleed fluid from line 222 to metering edges 334 and 336, respectively, formed on spool 226. The areas of metering edge 334 and 336 cooperating with their respective ports vary as a function of 1/62x where the x power corresponds to different values. Thus for illustration purposes, assume that the area of metering edge 334 is defined as 1/02X1 and the area of metering edge 336 is defined as l/62X2. These areas, varying as a function of compressor inlet temperature as sensed by -bellows 228, communicate pressure in lines 330 and 332 with drain lines 338 and 340, respectively. This serves to control the pressure drops across fixed restrictors 342 and 344, respectively. Consequently, the cooperation between variable restriction 334 and fixed restriction 342 effectuates a multiplication for developing the pressure in line 330 which is a function of fuel flow Wf corresponding to 02m.' Likewise the pressure in line 332 established by variable restriction 336 and the fixed restriction 344 is made a function of the desired fuel fiow in accordance with 02X2. The pressure in lines 330 and 332 are bled to metering edges 343 and 346 formed on spool 240', respectively, through lines 348 and 350, respectively. Metering edges 343 and 346 are contoured so that they will define in cooperation with the vadjacent port an area which is a function of N2/02. These metering edges serve to direct fluid from lines 348 and 350 into line 352 to give the proper temperature limit schedule for N2/92, and therefore the proper selection of 192"y has been made.

From the foregoing, it is apparent that one end of the spooly disposed in valve 246 is subjected to the scheduled overtemperature limit and the other to the scheduled surge limit, and the least pressure value of the two is transmitted to spool 188 of valve i182 shown in FIG. 3, where it is compared with the steady state signal.

OPERATION The operation of the fuel control can best be described by referring to FIG. 4 which is a graphical representation of the operation of the engine. It will lbe noted that the operation can be defined by the use of the control parameter derived hereinabove where W/Pg'zx is the ordinate, and N2/02 the abscissa, which is a rewritten expression for N/\/02. Curve M represents the temperature limit and curve N represents the surge limit of the acceleration schedule. Curve P represents the steady state engine operation and the plurality of curves R represents an infinite number of droop lines. Assuming that it is desirable to operate the engine at the speed indicated by numeral S which intersects the steady state line and the droop line and that the engine is just put in the on position. The pilot will cause levers 42 and 44 to rotate for establishing this condition which will automatically be achieved by the computing mechanism of the fuel control.

Immediately, fuel through line 30 will be fed to the minimum pressure and shutoff valve 68 and when its value overcomes the closing force thereof it will be injected into line 22 from where it is delivered to the burners. Simultaneously a signal generated by the steady state control mechanismv will cause the valve 50 to move towards wide open position. This condition is represented vby-line T. Immediately upon intersecting line M the temperature computing mechanism begins to take over the control of throttle valve 50 for limiting the fuel, which is accomplished by valves 200 and 234 and speed'sensor 150 together with the compressor discharge sensor 171.

The pressure established in line 176 is made proportional to compressor discharge pressure and is fed to line 256 to valve 200. Valve 200 which is responsive to compressor inlet temperature positions metering edge 250 metering fiuid into line 258. By virtue of the area defined by metering edge 250 with respect to the cooperating port which area is a function of 02X and the fixed restriction 260 a multiplication is effectuated so that the pressure in line 258 is made proportional to Pa/HZX. This pressure is then fed to valve 234 where metering edge 252 in conjunction with the cooperating port defines an area which varies as a function of Wf02X/P3. It will Ibe appreciated that the position of this valve is varied as a function of NgZ/@Z which has been established by metering edge 251 of spool 226. It will be appreciated that the pressure generated by pilot valve 161 is made proportional to Ng2, which, in turn, is fed to line 142 and admitted to metering edge 251. By virtue of metering edge 251 and fixed restriction 253 a division is effectuated so that the pressure in line 255 is made proportional t-o N2/62 which, in turn, acts on the left end of spool 240.

By virtue of the relationship of metering edge 252 and fixed restriction 262 another multiplication is effectuated so that the pressure in line 264 which, in turn is then admitted on the right end of spool 248 is made proportional to desired Wf. This causes a hydraulic signal to be `delivered through line 266 to act on the left end of spool 188 for causing it to shift and in turn alter the pressure in chamber 62. Owing to this pressure change, valve 50 is moved to a closing position for reducing the amount of fuel flow to maintain the limit defined by line At the point where line M intersects line N the surge limit of the acceleration schedule will take over the control. This is cffectuated by the mechanism enumerated in connection with the temperature limit except different metering edges are employed. Here the fluid pressure proportional to compressor discharge pressure is admitted to metering edge 224 via line 222. This .metering edge in cooperation with the -cooperating port defines an area which is a function of the V5; This metering edge together with fixed restriction 230 eifectuates a multiplication for establishing a pressure in line 232 Which is a function of Psv-zi This pressure in turn is fed to metering edge 238 which together with its cooperating port define an area which is a function of Wf/P3\/2. This area together with the area established by restrictor 242 effectuates still another multiplication for establishing the pressure in line 244 to be proportional to desired Wp VThis fluid is then admitted on the left end of spool 248 which, in turn, communicates a pressure signal to line 266 for adjusting the position of spool 188. This, in turn, causes the fluid in chamber 62 to be modified to position throttle valve in accordance with curve N.

At the point where curve N intersects once again line M the temperature control will konce again take When line M intersects droop line R the governor of i the steady state operation will take control. The angle of the droop .line is established by the component parts of the governor together with its attendant controlling mechanism.

From FIG. 4 it will be appreciated that fuel flow will be reduced until the control has established an operation condition indicated by the point S. This is the controlling point established by the computing mechanism of the fuel control.

As has been mentioned above, the free turbine speed is set by the pilot by virtue of the position of lever 44. The gas generator produces sufficient power to maintain the selected Ni. Should the free turbine run off speed, in the overspeed or underspeed direction, it will by virtue of the speed sensing mechanism cause valve 140 to readjust. This has the effect of resetting the speed of the gas generator an amount sufficient to change the power generated thereby for producing t-'he necessary energy of the working uid passing through the engine for driving the free turbine at the preselected speed.

Y THE HYDRAULIC MULTIPLICATION SYSTEM In order to establish the control pressure, it was necessary in several instances to perform a multiplication. This multiplication was effectuated by defining an area of a metering orifice tovary as a predetermined function. The following description is illustrative of how the hydraulic multiplication is effectuated.

The hydraulic multiplying device can be readily understood when thought of as a device which produces a pressure which is a percentage of some supply pressure. This device consists of iiowing fluid through two orifices in series as shown in FIG. 5.

If P supply represents one quantity and the y percent represents another, then P2 represents the product of these two and a multiplication has been achieved; where P represents the pressure value of the iiuid.

As P supply varies, P2 will vary as y% of P supply when the area of the orifice remains constant. As-the area of orifice 1 or 2 is varied, the percentage y will vary. It'can be seen now that variations in the quantities -to be multiplied can be controlled by either varying the P supply or the areas.

A further multiplication can be accomplished by next using P2 as the' supply pressure of another series of orifices as shown cascaded in FIG. 6.

This schematic represents the multiplication:

(l) P Supply (%A)=P2 perature)=%A, Wf/Pg/ (function of the engine speed)=%B and Wf (engine fuel iiow)=Pz.

In the interest of obtaining accuracy of the multiplication system, it may be necessary to design the orifices such that the cooperating orifices effectuating the multiplica- :tion have matching Reynolds number. This may be accomplished -by designing the cooperating orifices such vthat 'when the area of the orifices is at the midpoint of the control range, these orifices will be so shaped and sized so that the Reynolds number of each of the vorifices match each other. Also in the interest of obtaining accuracy of multiplication, the flow through metering edges 224 and 2Stdv will ybe much greater than that flowing through meteringV edges 238'and 252.

" White .this nventlon was illustrated utiliz-ing a hydrau- 16 lic type of computation system'for a fu'el control,i t-wi1l be obvious to one skilled'in the art that other medi-ums such as pneumatics or electronics and thelike may sluit-` ably be adapted to practice this invention. What is significant and contemplated by the scope of this'invention is the teaching of a new control parameter V/ftz s Pts @t2 for controlling a gas turbine engine. To this end-and referring now more specifically to FlG. 8, block 490 represents a suitable speed sensing devi-ce receivingl an input speed signal and converting it to a function of lthe square of the speed (N2). This signal is then fedlinto block 402 representing a divider which also receives a second input signal @responsive to the temperature at the inlet of the comp-ressor. Here these two signals are divided to produce an output signal equal to a function of N2/02. This signal then becomes the input signal to the function generator illustrated by block 404. It converts the signal 'to a Value which is a function of Wf/P3\/62. This signal is then multiplied in the multiplication box represented by numeral 4016 wh-ich multiplies this value by a signal equivalent to the function of P3\/02 which signal is established by block 4018. Block Hi8 which represents ra multiplication device receives a signal wh-ich is a function of compressor discharge pressure P3 and \/02 and multiplies `these two signals to generate the P3\/02 signal.4 s Block 406 multiplying these two values, then develops a Wf signalwhich is proportional to the amount of fuel established by the computation mechanisms. This signal is then fed to'a gate type of mechanism which senses another Wf signal developed by block 412. Gate mechanism 410 sensing these two input signals delivers the lower value of the two to a second gate mechanism 414. Block 412 represents a multiplier which multiplies the two input signals P3/92)c and Wf02X/P3. The Wf02X/P3 signal is developed by function generator illustratedby blo-ck 416, as follows.

Function generator 4116l responding to the input si-gnal N2/02 developed by divider 4012 modifies it toa value equal to a function of Wf02X/P3 which is then transmitted to m-ultiplier 412. The second lsignal Pa/HZX which is multiplied4 by multiplier 412 is generated by function generator 420 by combining two input signals P3 and 02X (generated by the function generator 422). The function generator 422 receives two input signals 02 and x (generated by function generator 424). The function generator 424 serves toV conVertN2/02 signal developed by divider 402 into the exponential x power. These two signals received by function generator 422 in turn establishes the signal 02X which is then combined with the P3 signal in function generator 420 for producing the P3/02X. The multiplication taking place in the multiplier 412 develops the Wf signal which is then transmitted to the gate mechanism 410. Gate mechanism 414 then compares the Itwo Wi signals and transmits the least plier 430 which multiplies P3 and Wf/P3 for developing the Wf signal.

From the foregoing, it is apparent that function generator 432 and multiplier 430 develop the scheduled steady state Wf value for controlling the engine during the steady state operation. Multiplier 412, function generator 416, function generator 422, multiplier 420 serve 17 to generate a Wf sign-al which establishes the overtemperature limit for the acceleration schedule. Function generator 424 serves to bias this signal as afunction of speed. Multipliers 408 and 406,'function generator 404 serve to generate a Wf signal for limi-ting surge' of `the acceleration schedule.

For a clearer understandingv of the mechanism'represented by the various blocks in FIG. 8, a graphical, illusrtration is shown therein to illustrate the desired function 'of each. For the sake lof simplicity and'convenienc'e and because the graphicalV illustrations are obvious to one skilled in the art, a description of each is omitted from herein,

Y, What has been described is a fuel control that assures accurate fuel metering to assure optimum engine performanceand assuring that malfunctions due to surge, overtemperature and rich and lean lflameout do not ensue. Thesfuel control monitors preselected engineoperating conditions and computes them to pro-duce a signal (Wf) whose value is proportional to the desired fuel flow.

The Wf signal -is computed as a function of Wf02X/P3 and Ng2/92. By virtue of this parameter, the heretofore customary three-dimensional cam has been eliminated which has led to the simplification of the fuel control resulting in a less complex and relatively less expensive control. Also, of relative importance is the fact that the temperature limit and the surge limit areV each independently adjustable.

It should be understood that, the invention is not limited to the particular embodiments shown and de-` where W f=weight of fuel flow per unit of time,

P=pressure of power plant working medium downstream of t-he compressor,

(Jr-compressor inlet temperature,

x=thermodynamic values of the power plant Working medium,A

N=rotational speed of the compressor.

2. The method of controlling a turbine type of power plant of the type having a combustion section, a compressor subject to surge driven by a turbine comprising the steps of pressurizing fuel, metering said pressurized fuel to the combustion section, and preventing surge by limiting the flow of fuel mentioned in the step of metering in accordance with a predetermined'schedule dened by a relationship of a single line function of N/ with respect to WfX/P so as to limit the turbine inlet temperature in a predetermined manner,

where Nzrotational speed of the compressor,

ezcompressor inlet temperature,

Wf=weight of fuel ow per unit of time,

P=compressor discharge pressure, and

x=functions of the thermodynamic characteristics of the power plant working medium.

3. The method of controlling a turbine power plant of the type having a combustion section, and a compressor driven by a turbine comprising the steps of pressurizing fuel, metering the pressurized fuel to the combustion section and limiting the temperature of the power plant working uidvby limiting .the ilowof fuelmentioned in the step of metering in accordance with a predetermined schedule defined by the formula WfX/R which varies as a single line function of N/\/5 so as to limit turbine inlet temperature in a predetermined manner,

where 4L The method of controlling a turbine type of power r plant of the type having a turbine, a combustion section,

and a compressor driven by the turbine comprising the steps of:

pressurizing fuel, sensing the parameters of compressor rotational speed, the pressure of the power plant working fluid, the temperature of the power plant workin-g fluid, computing the value of the parameters mentioned in the step of sensing to establish the formula WfHX/P as being a single line function of an engine parameter for limiting the turbine inlet temperature in a predetermined rn'anner,

where and metering the pressurized fuel to the combustion section in accordance with the formula established in the step of computing.

5. The method of controlling a turbinetype power plant of the type having -a combustion section, and a compressor subjected to surge driven by a turbine comprising the steps of: I

pressurizing fuel,

measuring power plant oper-ating parameters including a pressure of the power plant working fluid, a temperature of the power plant working fluid and a rotational speed of a rotating power plant member,

computing the power plant operating parameters measured in the step of measuring to esta'blish the single line relationship of WfX/P relative to N/\/l9` so as to-limit` turbine inlet temperature in a predetermined manner,

where Wf=weight of fuel flow per unit of time,

zcompressor inlettemperature,

x=a function of the thermodynamic characteristics of the power plant workingmedium,

P=compressor discharge pressure,

N=rotational speed of the compressor,

metering the pressurized fuel tothe combustion section in accordance to the relationship established in the step of computing, and preselecting the power output'of saidpower plant by adjusting the relationshipV established inthe step of computing as a function of a signal indicative of desired rotational rnember. 6. The method of controlling a turbine type of power plant of the type having a combustion section, a compressor driven by a turbine comprising the steps of:

pressurizing fuel, measuring power plant operating parameters of compressor `discharge pressure, compressor inlet temperature and compressor rotational speed, computing the parameters measured in the step of speed of the power plant rotating measuring to establish the single line relationship of WfX/P so as to -li-mit turbine inlet temperature in -a predetermined manner,

where Wf=weight of fuel ow per unit of time,

=compressor inlet temperature,

P=compressor discharge pressure,

x=a function of a thermodynamic characteristic of the power plant working medium,`

metering the pressurized fuel to the combustion section in accordance to the relationship established in the step of computing, and regulating the relationship established in the step of computing as a function of N/ \/0 where N :rotational speed of the compressor, 0=compressor inlet temperature.

7. The method of controlling a turbine type of power plant of the type having a turbine, a burner and a compressor driven by the turbine comprising the steps of:

pressurizing fuel,

metering the pressurized fuel to the burner, in accord- -ance with a predetermined schedule whereby Wfx/ P bears a predetermined single line relation to N/\/9 so as to limit turbine inlet temperature in a predetermined manner,

where Wf=weight of fuel per unit of time,

N :rotational speed of the compressor,

P=pressure of power plant working medium downstream of the compressor,

0=compressor inlet temperature, land T4=turbine inlet temperature,

ATb=burner temperature rise,

T3=compressor `discharge temperature,

Kzratio of specic heat of the working medium, n=cornpressor eiciency,

%=slope of the speed line of the compressor in a graph plotting the pressure ratio versus the P air flow of the compressor.

8. The method of controlling la turbine type of power plant of the type having a turbine, a combustion section, a compressor driven by the turbine comprising the steps of:

pressurizing fuel, -measuring power plant operating parameters of compressor discharge pressure, compressor inlet temperature and compressor rotational speed,

computing the parameters measured in the step of measuring to esta'blish the single Vline relationship o-f WfX/P for limiting turbine inlet temperature in a predetermined manner,

where Wf=weight of fuel flow per unit of time, 0=compressor inlet temperature, P=compressor discharge pressure,

x L T3 K-i 1 1 ATb ATb 2K7, oW,

W3 [ja-n+1 where T Af=turbine inlet temperature,

ATb-:burner temperature rise,

T3=compressor disch-arge temperature,

K=ratio of specific heat of the working medium, n=compressor efficiency,

a :slope of the speed line of the compressor in a graph plotting the pressure ratio versus the P air flow of the compressorA metering the pressurized fuel to the combustion section in accordance to the relationship established in the step of computing, and regulating the relationship established in the step of computing as a function of N 0 where n N=rctational speed of the compressor.

9. For a turbine type power plant having a compressor, burner and turbine driven by the gases discharging from the lburner for driving said compressor comprising a source of `fuel under pressure, connection means interconnecting lsaid source and said burner, fuel metering in said connection means for regulating the ow of fuel in laccordance with a predetermined schedule whereby Wfx/ P bears a pre-determined single line relation to N/Vfor limiting turbine inlet temperature in a predetermined manner,

where N=rotational speed of the compressor,

Wfzweight of fuel per unit of time,

P=pressure of power plant working medium downstream of the compressor,

0=compressor inlet temperature, and

T4=turbine inlet temperature,

ATD-:burner temperature rise,

T3=compressor discharge temperature,

K=ratio of specific heat of the working medium, 17=compressor efficiency,

=slope of the speed line of the compressor in a graph plotting the pressure ratio versus the P air How of the compressor.

`where Wf=weight of fuel ow per unit of time, 6=compressor inlet temperature,

21 P=compressor discharge pressure, x=a function of a thermodynamic characteristic of the power plant Working medium,

and Afuel regulating means in said connecting means responsive to said combining means.

11. A fuel control for controlling a turbine type of power plant having a turbine, a combustion section, a compressor driven by s-aid turbine, a source of fuel under pressure, connection means interconnecting s-aid source and said combustion section,

means for measuring compressor discharge pressure for producing a first signal, p

means for measuring compressor inlet temperature for producing a second signal,

means for measuring compressor rotational speed for producing a third signal,

means for combining said first, second and third signals to establish the single line relationship of WfX/P relative to an engine parameter for limiting turbine inlet temperature in `a predetermined manner,

where Wf=weight of fuel flow per unit of time, =compressor inlet temperature, Pzcompressor discharge pressure,

where T4=turbine inlet temperature,

AThzburner temperature rise,

T3=comp`ressor discharge temperature,

K=ratio of specific heat of the working medium, 11=compressor efficiency,

yi=slope of the speed line of the compressor in a, graph PL plotting the pressure ratio versus the air flow of the compressor.

12. The method off controlling a turbine type of power plant of the type that has a turbine, a compressor driven by the turbine and a -burner lcomprising the steps of metering fuel to the burner in accordance with a predetermined schedule defined by the formula WfX/P which is a single line function relative to a function of N /\/0 for limiting turbine inlet temperature in a predetermined manner,

where Wf=weight of fuel flow per unit of time,

0=compressor inlet temperature,

P=pressure of power plant working medium downstream of the compressor,

N=rotationa1 speed of the compressor,

x=a function ofthe thermodynamic characteristics of the power plant working medium,

computing a value of said tformula by measuring the speed of the compressor, compressor discharge pressure and compressor inlet temperature, whereby said value is computed by combining the value of lcompressor inlet temperature with a function of the speed of the compressor for producing a first signal,

generating a second signal as a function of the first signal whose relationship is defined Iby the formula WfX/P,

generating a third signal as -a function of the first signal for establishing the relationship defined by a value of the expression x,

22 combining the third signal with the value of compressor inlet temperature for producing -a fourth signal, combining the fourth signal with the value of cornpressor discharge pressure for producing a fifth signal, and combining the fifth signal and the second signal. 13. The -method of controlling a turbine type of power plant of the type that has a turbine, a compressor driven by the turbine and a burner comprising the steps of:

metering fuel to the burner in accordance with a predetermined schedule defined by the formula Win9x/P which is a single line function relative to a function of N/V for limiting turbine inlet temperature in a predetermined manner, where Wf=weight of fuel ow per unit of time,

N :rotational speed olf the compressor, P=pressure of power plant working medium, 0=compressor inlet temperature, and

T4=turbine inlet temperature,

ATb=burner temperature rise, T3=compressor discharge temperature,

K=ratio of spe'cic heat of the working medium,

computing a value of said formula by measuring the speed of the compressor, compressor discharge pressure and compressor inlet temperature, whereby said value is computed by l combining the value of compressor inlet temperature with a function of the speed of the compressor for producing a first signal, generating -a second signal as a function of the first signal whose relationship is defined by the formula WfX/P, generating Ia third signal as a function of the first signal for establishing the relationship defined by a value ofthe expression x, combining the third signal with the value of compressor inlet temperature for producing a fourth signal, com'bining the fourth signal with the Value of compressor `discharge pressure for producing a fifth signal, land combining the fifth signal and the second signal.

References Cited by the Examiner U NITED STATES PATENTS 2,668,416 2/1954 Lee 60-3928 2,933,130 4/1960 Wright et al 60-3928 X 2,954,669 10/1'960 Williams to- 39.28 3,032,986 5/1962 Wright 60-39'28 3,076,312 2/1963 Haigh 60-39.28 3,098,356 7/1963 Ioline 60-39.28 3,139,727 7/1964 Torell `60-3928 3,152,444 10/1964 Peczkowski et al. 60--39.l6

JULIUS E. WEST, Primary Examiner. 

1. THE METHOD OF CONTROLLING A TURBINE TYPE OF POWER PLANT OF THE TYPE HAVING A BURNER AND A COMPRESSOR DRIVEN BY A TURBINE COMPRISING THE STEPS OF PRESSURIZING FUEL, METERING THE PRESSURIZED FUEL TO THE BURNER AS A SINGLE LINE FUNCTION OF W10X-P RELATIVE TO N/$ SO AS TO LIMIT THE TURBINE INLET TEMPERATURE IN A PREDETERMINED MANNER, 